I told the compiler to go through a loop while a certain expression evaluates to true. When the expression evalates to false, the loop should terminate. If I had provided no expression, or I had provided true, or some value that would always evaluate to true, then I would expect the compiler to do as I tell it.
I have provided an expression for the loop to terminate that could evaluate to false, yet will never evaluate to false. This determination can be done through static analysis. Hence, I am still convinced that the compiler should issue a warning. Yet, I am still looking for a contradiction to my theory. On Tue, Apr 20, 2010 at 08:30:42PM -0700, Matthew Holland wrote: > It's not the compiler's job to tell you what you want, it's your job > to tell it! The -Wall flag doesn't mean, "warn me about every > possible stupid construct I can come up with." > > In all seriousness, if you don't get over using a "greater than or > equal" construct for loop termination, you're going to be in a world > of hurt if STL containers ever cross your transom. Just don't do > that, and everything will be fine. > > Matt > > On Tue, Apr 20, 2010 at 7:44 PM, Brian Lavender <[email protected]> wrote: > > On Tue, Apr 20, 2010 at 06:54:33PM -0700, Bill Broadley wrote: > >> On 04/20/2010 06:37 PM, Brian Lavender wrote: > >> > Our new guy (forget his name, doh!) and I figured out the problem with > >> > my loop that would count down, but not terminate. Turns out I was using > >> > an unsigned integer for my counter in my for loop and it is always > >> > greater than zero (Example 1). > >> > >> No, it's not always greater than zero. Your test says i>=0 so if it's > >> greater than or equal to zero it continues. Seems like you want i>0. > > > > Sorry, I meant to say it's always greater than or equal than zero. zero > > minus 1 is 4294967295 (0xffffffff) on a 32 bit machine. It can never go > > negative because it is unsigned and the loop will never terminate. Thus, > > I am thinking that the compiler could catch this due to the fact that i > > is unsigned. I wanted to print out the reverse of an array. > > > > If you run the following, the loop will never terminate. > > > > #include <stdio.h> > > > > int main() { > > int a[] = {5,6,8,3,4}; > > unsigned int i; > > > > > > for (i= (sizeof(a) -1)/sizeof(int) ; i >= 0; i--) { > > printf("%d\n",a[i]); > > } > > > > return 0; > > } > > > >> > >> > Funny thing is that -Wall didn't catch this. Seems that -Wall could > >> > catch this assuming that we want to loop to terminate. Any thoughts? > >> > >> Seems strange, but legal to do what you wanted. > >> > >> > Say the compiler gave a warning, would that mess up the "for (;;)" > >> > construct shown in Example 2? > >> > > >> > brian > >> > > >> > // Example 1 > >> > // Loop never terminates > >> > #include<stdio.h> > >> > > >> > int main() { > >> > unsigned int i, num=50; > >> > > >> > > >> > for (i= num ; i>= 0; i--) { > >> > printf("%u\n",i); > >> > } > >> > > >> > return 0; > >> > } > >> > > >> > // Example 2 > >> > // Purposely never terminates > >> > #include<stdio.h> > >> > > >> > int main() { > >> > for (;;) { > >> > printf("Hello forever\n"); > >> > } > >> > return 0; > >> > } > > > > > > > > -- > > Brian Lavender > > http://www.brie.com/brian/ > > > > "For every complex problem there is an answer that is clear, simple, and > > wrong." > > - H. L. Mencken > > _______________________________________________ > > vox-tech mailing list > > [email protected] > > http://lists.lugod.org/mailman/listinfo/vox-tech > > > _______________________________________________ > vox-tech mailing list > [email protected] > http://lists.lugod.org/mailman/listinfo/vox-tech -- Brian Lavender http://www.brie.com/brian/ "For every complex problem there is an answer that is clear, simple, and wrong." - H. L. Mencken _______________________________________________ vox-tech mailing list [email protected] http://lists.lugod.org/mailman/listinfo/vox-tech
